Please Help- Radioactive Isotopes?

Question

Imagine that you were studying a primitive organism found on mars. Within this organsim, there are 2 compounds that look like promising possibilities for the hereditary material of the organism. Each compound contains an element NOT found in the other.
How could you use radioactive isoptopes to determine which of the 2 componds is replicated as the cells of the organism replicate & divide?
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I don't really understand the uses of radioactive isotopes, I've been trying to read up on it- but it still doesn't make complete sense & I'm not quite sure how to apply it to situations like the one above. Can someone please help explain it to me. I would really appreciate it. Thank You! = )

Answer 1

An isotope is an atom of the same element (same number of protons), with a different number of neutrons. Chemically, it interact in exactly the same way with other atoms to form molecules.

A radioactive isotope is one that is unstable and becomes something else when a neutron turns into a proton and an electron (the atom becomes a new element) or when two protons and two neutrons are ejected from the nucleus (the atom becomes a new element). For example, Carbon-14 (6 protons and 8 neutrons) turns into Nitrogen-14 (7 proton, 7 neutrons).

In general, when organic material is formed, it contains a fixed mixture of isotopes of the same element. For example, organic molecules that contain lots of carbon atoms, will contain 1 atom of carbon-14 for each trillion atoms of carbon-12 at the moment they are created (this proportion is true if they are created on Earth, of course).

Then, the Carbon-14 slowly turns to Nitrogen-14 (while the Carbon-12 remains stable). Therefore, in older material, the proportion of Carbon-14 will be less than 1 in a trillion. Knowing exactly how much less can let you know the time that has elapsed.

Therefore, on Earth, fresher organic material will contain more Carbon-14 (in proportion to Carbon-12) than older material. I do not know what the isotope mixture would be for material on Mars, but the principle would remain the same: there would be one radioactive isotope that is present in higher quantity in fresher material than in older material.

Answer 2

While Raymond's answer on Radioisotopes is correct as far as it goes, he didn't answer your question completely. The way radioisotopes would be used in this instance is as follows. Apparently you have a way to isolate and identify the unique areas in these 2 compounds. There for by growing the organisms in two different environments one containing a radioisotopic form of one of the unique elements and the other containing a radioisotope form of the other unique element.

After a period of time the compound that is the genetic material, so to speak, will incorporate the radioisotope labeled element while the other will not. After isolating the compounds from each group of organisms, you then put them in a machine that recognizes the radioactivity. Both will probably show some radioactivity but the one that was replicated should be much higher than the one that isn't.

Unless it is like our RNA and DNA then I would guess that the higher amount of radioactivity would be in the RNA. Since DNA is only replicated once when the cells divide but RNA is made to produce proteins needed. If this is the case I would make sure you only let the organisms divide once that will really keep the radioactivity ratio higher to the non-replicating comound.